The integrated action of hormones controls the male and female sexual development, and reproductive cycle of female including pregnancy, parturition, and lactation. The reproductive system integrates with nervous control that sends impulses to secrete hormones and to release eggs, and sperm.
Hormones play a role in males and females to prepare their bodies to behave in a certain way once puberty begins.
In males, at the onset of puberty, the brain begins secreting GnRH, or gonadotropin-releasing hormone. In response, the pituitary gland releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH enters the testes to begin facilitating spermatogenesis. LH also enters the testes to make and release testosterone into the testes and the blood.
Testosterone, the hormone responsible for the secondary sexual characteristics, stimulates spermatogenesis, or the process of sperm production in the testes.
Hormonal regulation of the male reproductive system: GnRH stimulates the production of FSH and LH, which act on the testes to begin spermatogenesis and to develop secondary sex characteristics in the male. In turn, the testes production of testosterone and the hormone inhibin inhibit the release of GnRH, FSH, and LH in a negative feedback loop.
Consequently, the control of reproduction in females is more complex than that of the male. Aside from the hormone GnRH, FSH and LH, estrogens and progesterone are released from the developing follicles, which are structures on the ovaries that contain the maturing eggs.
FSH stimulates the development of egg cells, called ova. Follicle cells produce the hormone inhibin, which inhibits FSH production. LH also plays a role in the development of ova, as well as in the induction of ovulation and stimulation of estradiol and progesterone production by the ovaries. Estradiol and progesterone are steroid hormones that prepare the body for pregnancy. They assist in endometrial regrowth, ovulation, and calcium absorption; Estradiol is also responsible for the secondary sexual characteristics of females that include breast development, flaring of the hips, and a shorter period necessary for bone maturation.
Hormonal control of the female reproductive cycle: The ovarian and menstrual cycles of female reproduction are regulated by hormones produced by the hypothalamus, pituitary, and ovaries. The pattern of activation and inhibition of these hormones varies between phases of the reproductive cycle.
The female reproductive cycle or menstrual cycle is the physiological change that occurs in fertile women for sexual reproduction and fertilization. It is divided into three stages: the follicular phase, ovulation, and the luteal phase.
The follicular phase begins with an increase in FSH, which causes an increase in GnRH. This stage is where the follicles in the ovary mature and get ready for ovulation.
Ovulation is the process by which a mature ovarian follicle ruptures and discharges an ovum (oocyte). A spike in the amount of FSH and LH released from the pituitary gland triggers ovulation.
The luteal phase begins with the formation of the corpus luteum stimulated by FSH and LH and ends in either pregnancy or luteolysis. The main hormone associated with this stage is progesterone.
Stages of the menstrual cycle: Rising and falling hormone levels result in the progression of the ovarian and menstrual cycles.
After ovulation, the ruptured follicle becomes a corpus luteum, which secretes progesterone to either regrow the uterine lining or to support the pregnancy if it occurs. Hormones such as estrogens and progesterone are responsible for most of the changes experienced during pregnancy. Estrogen maintains the pregnancy, promotes fetal viability, and stimulates tissue growth in the mother and developing fetus. Progesterone prevents new ovarian follicles from developing and suppresses contract in uterine.
During childbirth, the pituitary hormone oxytocin is responsible for the contraction of the uterus at the beginning of labor. As labor nears, oxytocin begins to stimulate stronger, more painful uterine contractions, which is a positive feedback loop, stimulate the secretion of prostaglandins from fetal membranes.
In lactation, two main hormones are involved, prolactin and oxytocin. The presence of high prolactin levels abundantly stimulates milk production. Oxytocin triggers the cells to squeeze the milk from the breast.
The reproductive systems integrate with nervous control. The nervous system directly controls both the endocrine and reproductive system and organs related to them. It sends the impulses to secrete hormones and to release eggs and sperm. The reproductive system receives impulses from the nervous system and hormones from the endocrine system.
Practice Questions
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MCAT Official Prep (AAMC)
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Key Points
• The male and female reproductive system is regulated by FSH and LH produced by the pituitary gland in response to GnRH from the hypothalamus.
• FSH stimulates sperm maturation in males while it promotes egg maturation in females.
• In females, aside from the hormone GnRH, FSH and LH, estrogens and progesterone are released from the developing follicles.
• The female reproductive cycle or menstrual cycle is the physiological change that occurs in fertile women for sexual reproduction and fertilization; it is divided into three stages, namely, the follicular phase, ovulation, and the luteal phase.
• The hormones in control during pregnancy are estrogens and progesterone; In parturition, the pituitary hormone oxytocin is responsible for the contraction of the uterus at the beginning of labor; In lactation, two main hormones are involved, prolactin and oxytocin.
• The reproductive systems integrate with the nervous control by sending the impulses to secrete hormones, and to release eggs, and sperm.
Key Terms
estrogen: a hormone responsible for the appearance of secondary sex characteristics of human females at puberty and the maturation and maintenance of the reproductive organs in their functional state
estradiol: a potent estrogenic hormone produced in the ovaries of all vertebrates; the synthetic compound is used medicinally to treat estrogen deficiency and breast cancer
progesterone: a steroid hormone secreted by the ovaries that prepare the uterus for the implantation of a fertilized ovum and subsequent pregnancy
luteolysis: structural and functional degradation of the corpus luteum, which occurs at the end of the luteal phase of both the oestrous and menstrual cycles in the absence of pregnancy
testosterone: steroid hormone secreted by the male testes and important in the maturation of sperm cells, growth and development of the male reproductive system, and the development of male secondary sex characteristics
corpus luteum: a mass of cells that forms in an ovary
labor: the process of childbirth
gonadotropin-releasing hormone (GnRH): a hormone that controls the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone
follicle-stimulating hormone: hormones essential to pubertal development and the function of women’s ovaries and men’s testes.
luteinizing hormone: a hormone produced by gonadotropic cells in the anterior pituitary gland. In females, an acute rise of LH triggers ovulation and development of the corpus luteum
spermatogenesis: the process by which haploid spermatozoa develop from germ cells
ova: egg cell
ovulation: the release of an egg during menstruation in females
oxytocin: a hormone and that plays a role in social bonding, sexual reproduction, childbirth
prostaglandins: a group of lipids made at sites of tissue damage or infection that are involved in dealing with injury and illness
